1. Field of the Invention
The present invention relates to a vacuum pump, typically a turbo molecular pump used in a semiconductor manufacturing apparatus. In particular, the present invention relates to a vacuum pump in which damage to a rotor occurring due to a corrosive gas is prevented, thereby increasing the reliability and safety of the pump and peripheral apparatuses.
2. Description of the Related Art
As means for exhausting corrosive gasses from vacuum chambers, vacuum pumps such as turbo molecular pumps are used during semiconductor manufacturing processes such as dry etching and CVD.
FIG. 6 shows the basic structure of a conventional vacuum pump. A rotor 2 having a plurality of blade-like rotor blades 1 that are processed integrally along an upper outer circumference thereof, and a rotor shaft 3 attached integrally on a rotation center axis of the rotor 2 are accommodated inside a pump casing 4.
The rotor shaft 3 is rotatably supported through a bearing 6 in a stator column 5 that protrudes from a stator base 13 supporting the pump casing 4. Further, a driving motor 7 is inserted between the stator column 5 and the rotator shaft 3, and the rotor shaft 3 and the rotor 2 are rotated at high speed by the driving motor 7.
In addition, a plurality of blade-like stator blades 10 disposed alternately between the rotor blades 1 are imposed in an internal circumferential surface of the pump casing 4 through spacer rings 10a. Gas is sucked up from an inlet port 8 above the rotor 2 due to interaction between the rotor blades 1 rotating at high speed and the stator blades 10. The gas is exhausted to an exhaust port 9 below the rotor 2, so that the inside of a semiconductor processing vacuum chamber 14 connected to the inlet port 8 is placed in a high vacuum state.
Further, a rotating cylindrical surface 2b in an outer circumference of a skirt portion 2a in a lower half portion of the rotor 2 is fixed within the pump casing 4, and a screw stator 11, which is in sliding contact with the rotating cylindrical surface 2b so as to surround it, is fixed within the pump casing 4. Within a helical shape thread groove 12 formed in the inner circumferential surface of the screw stator 11, gas molecules, which are sent downward while passing between the rotor blades 1 and the stator blades 10, are carried to the gas exhaust port 9 side by the rotating cylindrical surface 2b of the rotor skirt portion along the thread groove 12, and exhaustion of the gas being in a slightly reduced vacuum state is performed.
For cases in which a vacuum pump having this type of structure is used in semiconductor manufacturing processes, the pump is often exposed to halogenated gases (hereafter referred to as corrosive gases) that are generated during processing such as dry etching and CVD. An aluminum alloy is normally used as a material for the rotor blades 1, the rotor 2, the pump casing 4, the stator blades 10, and the like, and an anti-corrosive (corrosion resistance) plating process is performed on the surface of the aluminum alloy, thus imparting it with anti-corrosiveness property against the corrosive gasses.
However, there are limits to the anti-corrosive plating process; in actuality, corrosion due to the corrosive gasses proceeds in the rotor blades 1 and in the rotor 2 after long usage. In particular, centrifugal force acts on the rotor blades 1 and the rotor 2 due to high speed rotation, and there are cases in which cracks develop from corroded portions, and breakage of the rotor blades 1 and the rotor 2 develops.
If the rotor 2 breaks, then fragments of the rotor 2 are scattered due to the centrifugal force, and rotation of the motor is forcibly stopped. A large stress therefore develops in the stator column 5 as a reaction force, and the stator blades 10 and the pump casing 4 are deformed or damaged, and this may even affect bonding portions with the vacuum chamber 14. The vacuum state of the entire processing apparatus to which the vacuum pump is applied is destroyed, the processing apparatus itself may be damaged, and in addition, there is a concern that this will invite emission of the corrosive gas to the outside, leading to an accident.
In view of the above situation, an object of the present invention is to provide a vacuum pump having increased pump reliability and safety by preventing rotor breakage occurring due to corrosion.
In order to achieve the aforementioned object, the present invention of this specification is characterized in that it comprises: a hollow cylindrical pump casing which is provided with an intake port communicating with a vacuum chamber and has a plurality of stages of stator blades disposed on an inner circumferential surface thereof; a stator column accommodated and fixed inside the pump casing, for supporting a rotor shaft that rotates at high speed; a rotor integrated with the rotor shaft and having a plurality of stages of rotor blades disposed on an outer circumferential surface thereof such that the rotor blades are disposed alternately with the stator blades of the pump casing; and a balancer provided in the outer circumferential surface of the rotor, for performing rotor balancing during high speed rotation of the rotor; and that the balancer is attached to the outer circumferential surface of the rotor through a fragile portion that is weak with respect to corrosive gasses. When corrosion due to the corrosive gasses within a gas passageway has advanced beyond a fixed degree, the balancer falls off so that an unbalanced state of the rotor forcibly appears.
When the unbalanced state of the rotor develops, in a case where the rotor shaft is supported by a ball bearing, errors may be detected by providing a vibration sensor onto the rotor. Further, for cases in which the rotor shaft is rotationally supported on the stator side by a magnetic bearing, errors may be detected by a rotor shaft radial direction sensor (displacement sensor) mounted between the rotor shaft and the stator.
Driving of the driving motor may be stopped by a signal from the vibration sensor or the displacement sensor.
In accordance with the present invention, the balancer provided in the outer circumferential surface of the rotor is attached to the outer circumferential surface of the rotor so as to face the gas passageway, and in addition, the balancer is supported by the fragile portion which is weak with respect to corrosive gasses. Therefore, due to the fragile portion the balancer falls off when corrosion of the corrosive gas within the gas passageway has advanced beyond a certain degree, so that an unbalanced state can be made to forcibly appear in the rotor.
The rotor therefore falls off from the balancer due to the advancement of corrosion, and an unbalanced state develops in the rotor so that the driving motor stops due to an error detecting means. Thus, the stator blades and the pump casing, and therefore the vacuum system, do not break.
In addition, the balancer that possesses the aforementioned corrosion detecting function also has a balancing function for making the rotor maintain a suitable posture. A portion of the balancer may be simply cut out for performing rotor balancing, so that balance correction is easy to perform. Therefore, compared to conventional balance adjustment work performed by opening holes using a drill or the like, balancing can be completed simply and without lowering the ridigity of the rotor.
The present invention of this specification is characterized in that the fragile portion of the balancer is set in a smaller diameter than that of the balancer main body, and is pressured-fixed through an adhesive within a pinhole formed in the outer circumferential surface of the rotor.
The present invention of this specification is characterized in that the fragile portion of the balancer is set in a smaller diameter than that of the balancer main body, and that the balancer is screwed into the inside of a screw hole drilled in the outer circumferential surface of the rotor.
In accordance with the present invention, the balancer is provided with a corrosion detecting function and a balancing function. The balancer is provided on the outer circumferential surface of the rotor by inserting the balancer inside a pinhole formed in the outer circumferential surface of the rotor through an adhesive, or by fixing the balancer by a screw-in method inside a screw hole formed in the outer circumferential surface of the rotor. Therefore, when corrosion of the rotor advances due to a corrosive gas and the balancer falls off, rotor unbalance develops, so that an error is detected and the pump is stopped to prevent an accident. In addition, by exchanging only this balancer portion, other portions (such as the rotor and the rotor blades) can be reutilized.
The present invention of this specification is characterized in that the balancer is formed integrally with the rotor, and that masking is performed on the fragile portion between the rotor and the balancer main body during anti-corrosion plating of the rotor.
In accordance with the present invention, the balancer is formed integrally with the rotor and possesses a corrosion detecting function and a balancing function. The fragile portion has a small diameter and masking is performed on this portion during anti-corrosive plating of the rotor, making the fragile portion a non-plated portion. This portion can therefore easily be imparted with a function as a fragile portion that is weak with respect to corrosive gasses.